Benchmarked Intrinsic Olefin Metathesis Activity: Mo vs. W

Combining Surface Organometallic Chemistry with rigorous olefin purification protocol allows evaluating and comparing the intrinsic activities of Mo and W olefin metathesis catalysts towards different types of olefin substrates. While well‐defined silica‐supported Mo and W imido‐alkylidenes show very similar activities in metathesis of internal olefins, Mo catalysts systematically outperform their W analogs in metathesis of terminal olefins, consistent with the formation of stable unsubstituted W metallacyclobutanes in the presence of ethylene. However, Mo catalysts are more prone to induce olefin isomerization, in particular when ethylene is present, probably because of their propensity to undergo more easily reduction processes.     

Unprecedented Selectivity of Ruthenium Iodide Benzylidenes in Olefin Metathesis Reactions

The development of selective olefin metathesis catalysts is crucial to achieving new synthetic pathways. Herein, we show that cis‐diiodo/sulfur‐chelated ruthenium benzylidenes do not react with strained cycloalkenes and internal olefins, but can effectively catalyze metathesis reactions of terminal dienes. Surprisingly, internal olefins may partake in olefin metathesis reactions once the ruthenium methylidene intermediate has been generated. This unexpected behavior allows the facile formation of strained cis‐cyclooctene by the RCM reaction of 1,9‐undecadiene. Moreover, cis‐1,4‐polybutadiene may be transformed into small cyclic molecules, including its smallest precursor, 1,5‐cyclooctadiene, by the use of this novel sequence. Norbornenes, including the reactive dicyclopentadiene (DCPD), remain unscathed even in the presence of terminal olefin substrates as they are too bulky to approach the diiodo ruthenium methylidene. The experimental results are accompanied by thorough DFT calculations.     

Asymmetric cyclization of omega-formyl-1,3-dienes catalyzed by a zerovalent nickel complex in the presence of silanes

A nickel(0)-catalyzed asymmetric cyclization of omega-formyl-1,3-diene in the presence of silanes in which five- or six-membered carbocycles or pyrrolidine derivatives were afforded up to 86% ee by the use of (2R,5R)-2,5-dimethyl-1-phenylphospholane as a monodentate chiral ligand was investigated. The reaction course of this asymmetric cyclization can be explained for by two possible mechanisms: one in which the cyclization proceeds via a pi-allylnickel intermediate to produce a cyclized product having an internal olefin in the side chain, and one in which the cyclization proceeds via a sigma bond metathesis of silane and the nickel-oxygen bond of oxanickelacycle to produce a cyclized compound having a terminal olefin and/or an internal olefin in the side chain. It was speculated that both of these mechanisms operate in this asymmetric cyclization depending upon the nature of silanes and the reaction conditions.     

The sulfinyl moiety as an intramolecular nucleophile. Part 3: Synthesis of (−)-muricatacin

A short, efficient and highly stereoselective synthesis of (−)-(R,R)-muricatacin is reported. The key steps include a highly diastereoselective reduction of a β-ketosulfoxide to a β-hydroxy sulfoxide, regio- and stereoselective bromohydration of an olefin employing the sulfinyl group as an internal nucleophile and chemoselective reduction of a double bond in the presence of a halogen atom.     

Phenanthrene synthesis by iron-catalyzed [4+2] benzannulation between alkyne and biaryl or 2-alkenylphenyl Grignard reagent

The [4+2] benzannulation reaction of internal or terminal alkynes with 2-biaryl, 2-heteroarylphenyl, or 2-alkenylphenyl Grignard reagents in the presence of Fe(acac)(3), 4,4'-di-tert-butyl-2,2'-bipyridyl, and 1,2-dichloro-2-methylpropane takes place at room temperature in 1 h to give 9-substituted or 9,10-disubstituted phenanthrenes and congeners in moderate to excellent yields. The reaction tolerates sensitive functional groups such as bromide and olefin. When applied to a 1,3-diyne, the annulation reaction takes place on both acetylenic moieties to give a bisphenanthrene derivative.     

Direct synthesis of soluble,end-functionalized polyenes and polyacetylene block copolymers

The ring-opening metathesis polymerization (ROMP) of 1,3,5,7-cyclooctatetraene (COT) in the presence of a chain transfer agent (CTA) with a highly active ruthenium olefin metathesis catalyst resulted in the formation of soluble polyenes. Small molecule CTAs containing an internal olefin and a variety of functional groups resulted in soluble telechelic polyenes with up to 20 double bonds. Use of polymeric CTAs with an olefin terminus resulted in polyacetylene block copolymers. These materials were subjected to a variety of solution and solid phase characterization techniques including (1)H NMR, UV/vis, and FT-IR spectroscopies, as well as MALDI-TOF MS and AFM.     

Palladium(II)-catalyzed aerobic hydroalkoxylation of styrenes containing a phenol

An intermolecular Pd-catalyzed hydroalkoxylation of styrenes that contain a phenol is presented. The reaction can be performed on terminal, disubstituted, and trisubstituted olefins in a variety of alcoholic solvents. Initial mechanistic data suggest a mechanism that involves oxidation of the alcoholic solvent to provide a Pd-hydride that inserts into an olefin. This is followed by formation of a quinone methide and subsequent addition of an alcohol to yield the hydroalkoxylated product.     

Palladium‐Catalyzed Oxidative Cross‐Coupling of α‐Cyanoketene Dithioacetals with Olefins

Efficient palladium‐catalyzed cross‐coupling reactions of the internal olefins α‐cyanoketene dithioacetals with a variety of olefins were achieved in dioxane/HOAc/DMSO (9:3:1 v/v/v) under air atmosphere or by means of AgOAc as the terminal oxidant. Electron‐deficient terminal olefins reacted to form the linear diene derivatives with air as the oxidant. Styrenes underwent the cross‐coupling to give both the linear and branched dienes when using AgOAc as the oxidant. Unactivated cyclic and linear internal olefin substrates both reacted in the presence of a catalytic amount of benzoquinone in air to produce skipped dienes. The typical products were structurally confirmed by X‐ray crystallography.     

Bis(Cyclic Alkyl Amino Carbene) Ruthenium Complexes: A Versatile,Highly Efficient Tool for Olefin Metathesis

The state‐of‐the‐art in olefin metathesis is application of N‐heterocyclic carbene (NHC)‐containing ruthenium alkylidenes for the formation of internal C=C bonds and of cyclic alkyl amino carbene (CAAC)‐containing ruthenium benzylidenes in the production of terminal olefins. A straightforward synthesis of bis(CAAC)Ru indenylidene complexes, which are highly effective in the formation of both terminal and internal C=C bonds at loadings as low as 1 ppm, is now reported.     

Bis(Cyclic Alkyl Amino Carbene) Ruthenium Complexes: A Versatile,Highly Efficient Tool for Olefin Metathesis

The state‐of‐the‐art in olefin metathesis is application of N‐heterocyclic carbene (NHC)‐containing ruthenium alkylidenes for the formation of internal C=C bonds and of cyclic alkyl amino carbene (CAAC)‐containing ruthenium benzylidenes in the production of terminal olefins. A straightforward synthesis of bis(CAAC)Ru indenylidene complexes, which are highly effective in the formation of both terminal and internal C=C bonds at loadings as low as 1 ppm, is now reported.     

Ring-closing metathesis and palladium-catalyzed formate reduction to 3-methyleneoxepanes. Formal synthesis of (−)-zoapatanol

A sequence of ring-closing metathesis and palladium-catalyzed formate reduction was developed for preparing O-heterocycles with an exocyclic olefin and applied to the asymmetric synthesis of zoapatanol. The key vicinal stereocenters in zoapatanol were constructed from the l-malic acid-derived lactone by successive chelation-controlled addition of alkyl groups. The O-allylations to prepare the dienes for RCM were achieved with the tertiary alcohols bearing internal olefins. The ring opening of oxepane, a new reaction pathway for the Pd-formate reduction, is also reported.     

Transannular macrocyclization via intramolecular B-alkyl Suzuki reaction

[reaction: see text]Transannular macrocyclizations via intramolecular B-alkyl Suzuki reactions are described. Regioselective terminal olefin hydroboration with 9-BBN followed by Pd(0)-catalyzed Suzuki reaction in the presence of a base such as TlOEt at high dilution generates macrocycles with a high degree of control over olefin geometry with isomerically pure E or Z vinyl iodide substrates. These reactions are complementary to ring closing metathesis (RCM) macrocyclizations and may prove superior in cases where control of olefin geometry is required.     

Oxidative coupling of NH isoquinolones with olefins catalyzed by Rh(III)

Rh(III)-catalyzed oxidative coupling reactions between isoquinolones with 3-aryl groups and activated olefins have been achieved using anhydrous Cu(OAc)(2) as an oxidant to give tetracyclic products. The nitrogen atom acts as a directing group to facilitate ortho C-H activation. This reaction can be one-pot starting from methyl benzohydroxamates, without the necessity of the isolation of isoquinolone products. A broad scope of substrates has been demonstrated, and both terminal and internal activated olefins can be applied. In the coupling of N-methylmaleimide, a Wacker-like mechanism was proposed, where backside attack of the NH group in isoquinolones is suggested as a key step. Selective C-H activation has also been achieved at the 8-position of 1-naphthol, leading to an olefination product.     

Reductive Decarboxylative Alkynylation of N‐Hydroxyphthalimide Esters with Bromoalkynes

A new method for the synthesis of terminal and internal alkynes from the nickel‐catalyzed decarboxylative coupling of N‐hydroxyphthalimide esters and bromoalkynes is presented. This reductive cross‐electrophile coupling is the first to use a C(sp)−X electrophile, and appears to proceed via an alkynylnickel intermediate. The internal alkyne products are obtained in yields of 41–95 % without the need for a photocatalyst, light, or a strong oxidant. The reaction displays a broad scope of carboxylic acid and alkyne coupling partners, and can tolerate an array of functional groups, including carbamate NH, halogen, nitrile, olefin, ketone, and ester moieties. Mechanistic studies suggest that this process does not involve an alkynylmanganese reagent and instead proceeds through nickel‐mediated bond formation.     

Cu(I)-catalyzed diamination of conjugated dienes. Complementary regioselectivity from two distinct mechanistic pathways involving Cu(II) and Cu(III) species

Conjugated dienes can be diaminated at the internal and/or terminal double bonds using Cu(I) as catalyst and N,N-di-t-butyldiaziridinone (1) as nitrogen source. The regioselectivity is highly dependent upon the choice of Cu(I) catalyst and the substituents on diene substrates. The diamination likely proceeds via two mechanistically distinct pathways. The N-N bond of N,N-di-t-butyldiaziridinone (1) is first homolytically cleaved by the Cu(I) catalyst to form four-membered Cu(III) species A and Cu(II) radical species B, which are in rapid equilibrium. The internal diamination likely proceeds in a concerted manner via Cu(III) species A, and the terminal diamination likely involves Cu(II) radical species B. Kinetic studies have shown that the diamination is first-order in N,N-di-t-butyldiaziridinone (1), zero-order in olefin, and first-order in total Cu(I) catalyst, and the cleavage of the N-N bond of 1 by the Cu(I) catalyst is the rate-determining step. The internal diamination is favored by use of CuBr without ligand and electron-rich dienes. The terminal diamination is favored when using CuCl-L and dienes with radical-stabilizing groups.     

Enantioselective reductive coupling of 1,3-enynes to glyoxalates mediated by hydrogen: asymmetric synthesis of beta,gamma-unsaturated alpha-hydroxy esters

Catalytic hydrogenation of 1,3-enynes 1a-8a in the presence of ethyl glyoxalate at ambient pressure and temperature using a rhodium catalyst modified by (R)-(3,5-tBu-4-MeOPh)-MeO-BIPHEP results in highly regio- and enantioselective reductive coupling to furnish the corresponding alpha-hydroxy esters 1b-8b. As demonstrated by the elaboration of alpha-hydroxy ester 1b, the terminal and internal olefin moieties embodied by the diene side chain are subject to selective manipulation, one over the other.     

One-pot terminal alkene homologation using a tandem olefin cross-metathesis/allylic carbonate reduction sequence

A one-carbon homologation of terminal alkenes has been developed utilizing an olefin cross-metathesis followed by a palladium-mediated allylic carbonate reduction; various substrates were used to demonstrate the scope of the reaction, with yields ranging from 65 to 86%.     

Aromatic‐Amide‐Derived Olefins as a Springboard: Isomerization‐Initiated Palladium‐Catalyzed Hydrogenation of Olefins and Reductive Decarbonylation of Acyl Chlorides with Hydrosilane

A highly efficient catalytic protocol for the isomerization of substituted amide‐derived olefins is presented that successfully uses a hydride palladium catalyst system generated from [PdCl₂(PPh₃)₂] and HSi(OEt)₃. The Z to E isomerization was carried out smoothly and resulted in geometrically pure substituted olefins. Apart from the cis–trans isomerization of double bonds, the selective reduction of terminal olefins and activated alkenes was performed with excellent functional group tolerance in the presence of an amide‐derived olefin ligand, and the products were obtained in high isolated yields (up to >99 %). Furthermore, the palladium/hydrosilane system was able to promote the reductive decarbonylation of benzoyl chloride when a (Z)‐olefin with an aromatic amide moiety was used as a ligand.     

Ruthenium-catalyzed tandem cross-metathesis/Wittig olefination: generation of conjugated dienoic esters from terminal olefins

[reaction: see text] In the presence of ruthenium-based olefin metathesis catalysts and triphenylphosphine, alpha,beta-unsaturated aldehydes can be olefinated with diazoacetates. This ruthenium-catalyzed transformation has been employed in tandem with olefin cross-metathesis to convert terminal olefins into 1,3-dienoic esters in a single operation.     

Aromatic-amide-derived olefins as a springboard: isomerization-initiated palladium-catalyzed hydrogenation of olefins and reductive decarbonylation of acyl chlorides with hydrosilane

A highly efficient catalytic protocol for the isomerization of substituted amide-derived olefins is presented that successfully uses a hydride palladium catalyst system generated from [PdCl(2)(PPh(3))(2)] and HSi(OEt)(3). The Z to E isomerization was carried out smoothly and resulted in geometrically pure substituted olefins. Apart from the cis-trans isomerization of double bonds, the selective reduction of terminal olefins and activated alkenes was performed with excellent functional group tolerance in the presence of an amide-derived olefin ligand, and the products were obtained in high isolated yields (up to >99?%). Furthermore, the palladium/hydrosilane system was able to promote the reductive decarbonylation of benzoyl chloride when a (Z)-olefin with an aromatic amide moiety was used as a ligand.